Process for separating tantalum and columbium values



United States Patent PROCESS FOR SEPARATIN G TANTALUM AND COLUMBIUMVALUES John R. Ruhotf and George 'L. Martin, Webster Groves, and Charles0. Gerfen, Brentwood, Mo., assignors to Mallinckrodt Chemical Works, St.Louis, Mo., a corporation of Missouri N0 Drawing. Original applicationFebruary 15, 1955, Serial No. 488,403, now Patent No. 2,859,099, datedNovember 4, 1958. Divided and this application May 16, 1957, Serial No.659,467

1 Claim. or. 23-43 This invention relates to a separation process andmore particularly to a process for recovering tantalum values frommineral concentrates.

This application is a division of our copending application Serial No.488,403, filed February 15, 1955, now Patent No. 2,859,099, datedNovember 4, 1958.

Briefly, the present invention is directed to the method of upgradingtantalum-containing concentrates which comprises adjusting the fluorideion concentration of a mixture of said tantalum compound and a columbiumcompound to eifect the separation of hydrous tantalum oxide from themixture.

Among the several objects of this invention may be noted the provisionof improved methods for recovering tantalum values from mineralconcentrates containing a tantalum compound and a columbium compound;the provision of methods which yield a concentrate of tan talum valuesin reactive and readily usable form; and the provision of methods forrecovering tantalum from such concentrates without the use of expensivechemical reagents. Other objects and features will be in part apparentand in part pointed out hereinafter.

The invention accordingly comprises the methods hereinafter described,the scope of the invention being indicated in the following claim.

Known minerals containing tantalum also contain columbium. However, thechemical methods heretofore available for recovering tantalum valuesfrom concentrates containing tantalum values alone or associated withcolumbium have been inefficient, or required the use of expensivechemical reagents.

In accordance with the present invention, it has now been found thattantalum values can be conveniently and economically recovered fromconcentrates containing tantalum values alone or associated withcompounds of columbium by precipitating the tantalum values from asolution containing tantalum fluocomplex, using the hydrous oxide ofcolumbium as the precipitating agent. The amount of hydrous columbiumoxide added to the solution should not substantially exceed thatrequired to displace tantalum from its fluocomplex (including thatnecessary to react with any free fluoride or impurities which may bedisplaced by hydrous columbium oxide and which may have been presentinitially). If compounds of other elements (such as iron) which aredisplaced by columbium are present, appropriate allowance should be madein the amount of hydrous columbium oxide added. Compounds of suchelements can be easily removed from the precipitate by conventionalmethods.

Hydrous columbium oxide is preferably employed as the precipitatingagent although this oxide together with hydrous tantalum oxide may alsobe used as the precipitating agent. For example, the mixed hydrousoxides of columbium and tantalum may be obtained by precipitation from asolution of the fluocomplexes of these elements by addition of a base,such as ammonia. Thus, the mixed hydrous oxides of columbium andtantalum 2,895,793 Patented July 21, 1959 are suitable for use as theprecipitating agent and the presence of the hydrous oxide of tantalum insuch a mixture does not interfere with the practice of the invention.The process of the present invention also includes treatmg a mixture ofthe hydrous oxides of tantalum and columbium with suflicient fluoride toform only the fluocomplexes of columbium. In this case, the hydrousoxide of columbium is selectively dissolved from the mixture of hydrousoxides, but the principle for recovering tantalum values is the same asthat described above.

In carrying out the present invention, the fluoride ion concentration isadjusted to be equivalent to the amount of columbium present in themixture. In general, it is preferred that the process be carried out ata pH of 2-6. Columbium is present as CbOF in solution and the proportionof fluoride ions in the mixture is computed accordingly in determiningthe equivalent. At a pH above approximately 6, CbOF is not stable in theab sence of a large excess of fluoride which hinders the separation oftantalum from columbium.

The present process can be carried out by the addition of a suitableproportion of hydrous columbium oxide to a solution containing thefluocomplex of tantalum. The amount of such hydrous oxide added isdetermined upon the basis stated in the preceding paragraph. The hydrouscolumbium oxide added displaces the tantalum values from solution,thereby precipitating hydrous tantalum oxide, the columbium remaining insolution as its fluocomplex.

Alternatively, mixtures containing hydrous oxides of tantalum andcolumbium may be separated by adding to the mixture a source of fluorideions, the proportion there of being determined as outlined above, andadjusting so that the final pH is as stated above. A fluocomplex ofcolumbium is thereby formed which is Water soluble and may, therefore,be selectively dissolved from the mixture. It will be noted that, inthis instance, the resulting product is of the same character asoutlined in the preceding paragraph and is obtained by reason of thesame chemical principles.

If any compound of elements of group IV-B of the periodic table ispresent, this fact will not aflect the operation of the process exceptthat appropriate steps should be taken in adjusting the fluoride ionconcentration. The fluocomplexes of the group IV-B elements arerelatively more stable than the fluocomplexes of columbium and tantalum,and are therefore retained in solution.

It is often advantageous to heat the mixture while carrying out theprocess so as to increase the solubility of the fluocomplexes and makeit possible to Work with more concentrated solutions. Also, althoughalkali metal hydroxides can be used for adjusting the pH of the mixture,ammonia is usually preferred since ammonium salts are more soluble.

The following examples illustrate the invention.

Example 1 To an aqueous solution (50 ml.) of the fluocomplex of tantalumcontaining 40.0 g./liter of fluoride (expressed as NH HF and 43 g./literof tantalum (expressed as Ta O was added hydrous columbium oxide so thatthe mixture contained 40.0 g./liter of columbium (expressed as Cb O Thismixture contained fluoride equivalent to that required for formation of('NH CbOF The pH was adjusted to approximately 5.6 with ammonia, and themixture was stirred for one hour. The solid phase then contained 93% ofthe tantalum, and the ratio of tantalum to columbium in this phase was1.6 to 1.

Example 2 A solution of ammonium bifiuoride in water (2.0 g. in 50 ml.)was added to a mixture of the hydrous oxides of tantalum and columbium(equivalent to 2.15 g. Ta O and 2.0 g. Cb O The resulting mixturecontained fluoride equivalent to that required for formation of (NH CbOFThe pH was adjusted to approximately 5.6 with ammonia, and the mixturewas stirred for one hour. The solid phase then contained 98% of thetantalum, and the ratio of tantalum to columbium in this phase was 2.3to 1.

It will be understood that any convenient source of fluoride ions, suchas hydrofluoric acid or one of its watersoluble salts, may be used inthe practice of the present invention.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above methods without departingfrom the scope of the invention, it is intended that all mattercontained in the above description shall be interpreted as illustrativeand not in a limiting sense.

We claim:

The method of recovering tantalum values fi'om a concentrate containingthe hydrous oxides of tantalum and columbium, comprising adding a sourceof fluoride ions .4 to an aqueous suspension of said hydrous oxides inan amount sufiicient to selectively dissolve the hydrous oxide ofcolumbium as its fluocomplex but less than that required to dissolve thehydrous oxide of tantalum as its fluocomplex, the pH being maintained ata value between approximately 2-6, and separating the resulting solutioncontaining the fluocomplex of columbium from the undissolved hydrousoxide of tantalum.

References Cited in the file of this patent Thorpe: Dictionary ofApplied Chemistry, published by Longmans, Green and Co., New York, vol.II, 1916, page 123; vol. V (1916), page 401; vol. III (1939), pages310-11.

Balke: Electrochemical Society, Preprint 85-3, 1944, pp. 25-30.

Browning: Introduction to the Rarer Elements, published by J. Wiley andSons, New York, 1914, page 122.

Tantalum, in Chemical Engineering, September 1948, pp. 152-5.

Hampel: Rare Metals Handbook, publ. by Reinhold Publ. Corp., New York,1954, pages 390-1.

Pchelkina et al., in Chemical Abstracts, vol. 49, col. 1461(c), 1955.

